This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-109186, filed Apr. 16, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a fuel cell stack prepared by making integral a fuel cell laminate body consisting of a plurality of solid polymer type fuel cells each having a solid polymer membrane by a fastening means.
In recent years, the number of motor cars using gasoline engines has rapidly increased such that about two motor cars are owned nowadays by each family. Naturally, the exhaust gas discharged from the motor car attracts social attentions in relation to the air pollution problem. Under the circumstances, vigorous studies are being made in an attempt to use a fuel cell as a power source of a motor that is used in place of the internal combustion engine. The air pollution problem need not be worried about in the motor car using the fuel cell, which does not use a fossil fuel. In addition, noise is scarcely generated from the motor using the fuel cell. Also, the motor using the fuel cell is advantageous over the internal combustion engine in the energy recovery rate.
In using the fuel cell in a motor car, it is desirable for the fuel cell and the auxiliary facilities to be as small as possible, though an unduly large output is not required. Such being the situation, PEFC (polymer electrolyte fuel cell), in which a solid polymer membrane is sandwiched between two kinds of electrodes and these electrodes are wrapped in a separator, attracts attentions among various fuel cells.
FIG. 7 shows the basic construction of a solid polymer type fuel cell. As shown in the drawing, a cell body 1 comprises a solid polymer membrane 2. An oxygen electrode 3 and a hydrogen electrode 4 are attached to both surfaces of the solid polymer membrane 2 to form an integral structure. The integral structure is prepared by attaching the oxygen electrode 3 and the hydrogen electrode 4 to both surfaces of the solid polymer membrane 2, followed by applying a hot press to the resultant structure. A reaction membrane 5a and a gas diffusion membrane 6a are attached to both surfaces of the oxygen electrode 3 such that the reaction membrane 5a is in contact with the solid polymer membrane 2. Likewise, a reaction membrane 5b and a gas diffusion membrane 6b are attached to both surfaces of the hydrogen electrode 4 such that the reaction membrane 5b is in contact with the solid polymer membrane 2. The cell reaction takes place mainly between the solid polymer membrane 2 and the reaction membranes 5a, 5b. A separator 7 having oxygen supply grooves 7a is attached to the surface of the oxygen electrode 3. Likewise, a separator 8 having hydrogen supply grooves 8a is attached to the surface of the hydrogen electrode 4.
In the fuel cell of the particular construction, oxygen and hydrogen introduced through the oxygen supply grooves 7a and the hydrogen supply grooves 8a are supplied through the gas diffusion membranes 6a, 6b into the reaction membranes 5a, 5b, respectively. As a result, reactions given below take place at the interface A between the solid polymer membrane 2 and the reaction membrane 5a and at the interface B between the solid polymer membrane 2 and the reaction membrane 5b: 
Reaction at interface A: (1/2)O2+2H+xe2x86x92H2O
Reaction at interface B: H2xe2x86x922H+xe2x86x922exe2x88x92
The hydrogen ions (2H+) generated at the interface B flow from the hydrogen electrode 4 into the oxygen electrode 3 through the solid polymer membrane 2. On the other hand, the electrons (2exe2x88x92) generated at the interface B flow from the hydrogen electrode 4 into the oxygen electrode 3 through a load 9 so as to obtain an electric energy.
In the fuel cell of the construction described above, it is necessary for the separators 7 and 8 to supply an oxidizing gas and a fuel gas to the back surfaces of the oxygen electrode 3 and the hydrogen electrode 4, respectively, uniformly and in a completely separated manner. Also, it is necessary for the fuel cell to collect efficiently the electivity generated by the reaction. Further, since heat is generated by the cell reaction, it is necessary to release the reaction heat through the gas separators in order to stabilize the power generating operation. Various separators are proposed for meeting these requirements. FIG. 8 exemplifies the PEFC structure (fuel cell laminate body) using a plurality of separators S. In the fuel cell stack of the construction shown in the drawing, a fuel gas supply plate 19 is attached to an oxidizing gas supply plate 20 such that a fluid passageway 21 is defined between these supply plates 19 and 20. A cooling water is circulated through the fluid passageway 21 to suppress the temperature elevation caused by the reaction heat generated at the boundaries between the oxygen electrode and the solid polymer electrolyte plate and between the hydrogen electrode and the solid polymer electrolyte plate.
It was customary in the past to assemble the fuel cell stack 11 as shown in, for example, FIGS. 9 and 11. Incidentally, FIG. 11 is a plan view showing the fuel cell stack 11 shown in FIG. 9. The fuel cell stack 11 comprises a plurality of unit cells 10 stacked one upon the other in the vertical direction and upper and lower flanges 12, 13 somewhat larger than the unit cell 10 and positioned on the upper and lower surfaces, respectively, of the stack of the unit cells 10. Each of these upper and lower flanges 12, 13 is provided with a plurality of bolt holes positioned outside the stack of the unit cells 10. Fastening bolts 14 are inserted into the bolt holes to permit these bolts 14 to extend through the upper and lower flanges 12, 13, and nuts (not shown) are engaged at the end portions of the fastening bolts 14 so as to fasten the stack of the unit cells 10 held between the upper and lower flanges 12 and 13. Reference numerals 15 and 16 shown in FIG. 11 represent a cooling water supply hole and a cooling water discharge hole, respectively, which extend through the flanges 12, 13 and the fuel cell stack 11. Also, reference numerals 17 and 18 represent a reactant gas supply hole and a reaction gas discharge hole, respectively, which extend through the flanges 12, 13 and the fuel cell stack 11.
The conventional fuel cell laminate body is assembled as shown in, for example, FIG. 10 to constitute the fuel cell stack 11. The stack shown in FIG. 10 is equal to the stack shown in FIG. 9, except that, in FIG. 10, the flanges 12, 13 are equal in size to the unit cell 10.
The conventional fuel cell stack is defective in that, since a large number of fastening bolts 14 are used for fastening the fuel cell laminate body, the effective area ratio of the fuel cell stack is low. For example, where the fuel cell stack shown in FIG. 9 including the region of the fastening bolts 14 has a length Y1 of, for example, 140 mm, and a width T1 of, for example 120 mm, the region of the unit cell 10, which is shaded in FIG. 11, has a length Y2 of, for example, 130 mm, and a width T2 of, for example, 100 mm. It follows that the effective area ratio is: T2xc2x7Y2/T1xc2x7Y1={(100xc3x97130)/(120xc3x97140)}xc3x97100≈77%. Also, the conventional fuel cell stack is rendered heavier and more bulky.
Fuel cells are also disclosed in Japanese Patent Disclosure (Kokai) No. 10-189025 and Japanese Patent Disclosure No. 9-92324. JP ""025 is directed to a fuel cell in which the direction of the pressurizing force applied to the fuel cell stack housed in a case is kept parallel to the stacking direction of the unit cells so as to prevent the gas sealing properties from being deteriorated and to prevent the contact resistance from being increased. On the other hand, JP ""324 is directed to a fuel cell module and a fuel cell in which pushing force is applied to a laminate body of unit cells without using a fastening tool such as a bolt so as to make compact the fuel cell module and the fuel cell.
An object of the present invention is to provide a fuel cell stack, comprising a fastening means including support members equipped with flanges arranged at upper and lower edge portions of a fuel cell laminate body, connecting members joined to the support members and extending in the vertical direction of the fuel cell laminate body, and fastening tools for fastening the support members in the vertical direction of the fuel cell laminate body. The particular construction of the present invention makes it possible to increase the effective area ratio of the fuel cell stack, compared with the conventional fuel cell stack. In addition, the fuel cell stack of the present invention is light in weight and small in outer size.
According to the present invention, there is provided a fuel cell stack, comprising a fuel cell laminate body prepared by laminating a plurality of unit cells each having a solid polymer membrane sandwiched between electrodes and a fastening means for fastening the fuel cell laminate body in the direction of lamination of the unit cells, wherein the fastening means includes support members equipped with flanges and arranged at the upper and lower edges of the fuel cell laminate body, connecting members joined to the support members at the upper and lower end portions of the fuel cell laminate body, and fastening tools for fastening the support members in the vertical direction of the fuel cell laminate body.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.